The star was a long-term supporter of a number of charities - including Childline, the Terrence Higgins Trust and Macmillan Cancer Support - who could also be bequeathed large sums.
Michael's older sisters, Melanie and Yioda, his boyfriend Fadi Fawaz and his cousin Andros' two children, to whom he is also a godfather, are also expected to be named in his will.
As well as a large sums from royalties, Michael is understood to have been well paid to perform at private parties and events in the decade before his death.
He is understood to own at least four properties, including the Oxfordshire cottage where he died, his mansion in London and lavish homes in New York and Sydney.
As well as his four lavish properties, Michael is said to have invested his money in art with the help of his art dealer Goss.
Michael introduced Wham! bandmate Shirlie Holliman to Kemp and the couple married in 1988.
Kemp posted on Twitter yesterday: "My whole family and I are devastated at the loss of our beautiful friend Yog! We will miss him so much! We are all heartbroken!"
His son Roman also paid tribute to Michael, adding: "The man who toured the world with my mum; her best friend.
"The man who introduced my parents; who forced my mum to call my dad. The man that took me and Harley around the world; just to see us smile. The man we all love. We love you Yog."
Michael was hoping to enjoy a Boxing Day meal with Holliman and her family, her son told the Sun before Michael's death.
Roman said Michael was "family" to him and someone he had known his whole life. He said his mother, Holliman, still spoke to Michael every week before his death.
A friend of Michael's revealed this morning that George was considering a Wham! reunion.
Richard Blade, a US DJ who worked with the band, said Holliman had told him the pop band were considering getting back together for a one-off gig.
He told Radio Five Live: "It's such a shame that we have all been robbed of that chance to see a really, really fun pop band get back together."
Geri Horner, formerly Halliwell, was a long-term friend of Michael's and also told of her sadness on her Instagram page yesterday.
Next to a photo of her and the star, she wrote: "So so sad , R.I.P George, a dear friend, the kindest, most generous & talented person. My thoughts are with his family."
Geri is a close friend of Goss, who was described as the love of George Michael's life. The Spice Girls, now 44, star even moved in with the two men after she left the girl band in 1998.
She described the living arrangement as a "Will and Grace situation", in which she stayed for three months.
Michael was also godfather to James Kennedy, a British DJ who stars in US reality TV show Vanderpump Rules.
It is understood Kennedy had not seen Michael for some years after the singer and his father, Andros Georgiou, fell out following a row.
Kennedy posted a picture of himself and the star on his Instagram page yesterday, writing: "Rest In Peace George I'm heartbroken we never got to speak again after so many years."
Michael's boyfriend Fadi Fawaz found the star dead in his bed at his home in Goring on Sunday. Fawaz said he would "never forget" the terrible moment, adding: "I will never stop missing you".
The star had lived as a virtual recluse in recent months, following years of ill-health and battles with crack cocaine addiction.
The source told the Daily Telegraph: "He's been rushed to A&E on several occasions. He used heroin. I think it's amazing he's lasted as long as he has."
A 69-year-old neighbour, who asked to remain anonymous, said Michael was notably absent from the midnight mass Christmas Eve service at St Thomas of Canterbury church, the parish church opposite his home.
A neighbour at his home in North London, Sasha Gretsay, said he looked "tired" and "haggard" when she saw him in a restaurant earlier this year.
